Communication apparatus and communication method

ABSTRACT

A managing station comprises a delay time measuring unit that measures, while transmitting a delay time measurement frame to each of the slave stations and receiving a response frame responsive to the delay time measurement frame from the slave station, an elapsed time from when transmitting the delay time measurement frame to when receiving the response frame and that calculates a delay time of the slave station; and a delay detecting unit that compares the calculated delay time and a delay judgment value that is an average of the delay times calculated in a past for the slave station to determine whether delay is occurring in the slave station for each of the slave stations and that identifies, if delay is occurring in the slave station, the position of a delay element using connection configuration information indicating connection states between the communication apparatuses in the network.

FIELD

The present invention relates to a communication apparatus and acommunication method.

In conventional communication systems, in order for a managing stationto make slave stations synchronize in operation, the managing stationsends out a synchronization frame to each slave station, and the slavestation having received it starts processing upon the reception.

For example, where a communication system is formed of a line-typenetwork, the reaching time when the synchronization frame from themanaging station reaches the slave station differs for each slavestation due to the influence of transfer processing times in slavestations arranged in the path and transmission delay times in the cablesconnecting communication apparatuses.

In order to correct for the difference in the reaching time of thesynchronization frame, each slave station finds out the delay time thatit takes for the synchronization frame to reach the slave station, isgiven an offset value corresponding to the delay time, and adds theoffset value to the reaching time, thereby making synchronization timebe the same for each slave station. As the method with which each slavestation finds out the delay time, there is known a method that measuresthe transmission time of a particular signal sent back and forth betweenthe managing station and each slave station to obtain a transmissiondelay time from this transmission time (refer to, e.g., PatentLiterature 1).

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Application Laid-Open PublicationNo. H10-13394

SUMMARY Technical Problem

In the above conventional art, when unexpected delay has occurredbecause a slave station on the network has failed or a hub has beenadded, if the synchronization frame is sent out without a delay due tothat delay being taken into account, then the time when thesynchronization frame reaches slave stations subsequent to the failedslave station or the added hub, as seen from the managing station,becomes later, so that an event where the synchronization time is notthe same (loss of synchronization) occurs. However, there is the problemthat, if such an unexpected delay element has occurred, the occurredplace cannot be identified.

The present invention was made in view of the above facts, and an objectthereof is to provide a communication apparatus and communication methodwhich can detect the occurrence of unexpected delay and identify theoccurred place of the delay element in a communication system where amanaging station and multiple slave stations are connected viatransmission paths and where communication is performed with maintainingsynchronization between the slave stations.

Solution to Problem

There is provided a communication apparatus to be connected to aplurality of slave stations via a network and to manage a logical ringon the network and to communicate with the slave stations at apredetermined communication cycle, comprising: a communication unit thatcommunicates with the slave stations; a delay time measuring unit that,while transmitting a delay time measurement frame to each of the slavestations via the communication unit and receiving a response frame tothe delay time measurement frame from the slave station via thecommunication unit, measures elapsed time from when transmitting thedelay time measurement frame to when receiving the response frame, andcalculates a half of the measured elapsed time as a delay time of theslave station; and a delay detecting unit that compares the delay timecalculated by the delay time measuring unit and a delay judgment valuethat is an average of the delay times calculated in a past for the slavestation to determine whether delay is occurring in the slave station foreach of the slave stations, and identifies, if delay is occurring in theslave station, the position of a delay element using connectionconfiguration information indicating connection states between thecommunication apparatus and the plurality of slave stations in thenetwork.

Advantageous Effects of Invention

According to the present invention, when the delay time of a slavestation is greater than an average delay time measured in the past, itis determined that a delay element is occurring, and its place isidentified with use of connection configuration information. Hence, thepresent invention has the effect that if unexpected delay has occurredon the network because of a failure in or addition of a slave station,it can be immediately determined where the delay element has occurred.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram schematically showing an example of theconfiguration of a communication system according to an embodiment ofthe present invention.

FIG. 2 is a diagram schematically showing an example of theconfiguration of a managing station according to the embodiment.

FIG. 3 is a flow chart showing an example of the procedure of a delaytime measuring process.

FIG. 4 is a diagram showing the outline of the delay time measuringprocess.

FIG. 5 is a flow chart showing an example of the procedure of an averagedelay time calculating process.

FIG. 6 is a flow chart showing an example of the procedure of a delaydetecting process.

FIG. 7 is a diagram schematically showing an example of the operation ofthe communication system in the case where a delay element has occurredon the network.

FIG. 8 is a diagram schematically showing an example of the operation ofthe communication system in the case where a delay element has occurredon a line-type star-type mixed network.

DESCRIPTION OF EMBODIMENTS

A preferred embodiment of the communication apparatus and communicationmethod according to the present invention will be described in detailbelow with reference to the accompanying drawings. Note that thisembodiment is not intended to limit the present invention.

FIG. 1 is a diagram schematically showing an example of theconfiguration of a communication system according to the embodiment ofthe present invention. In the communication system, one managing station10 and multiple slave stations 30 (30A to 30D) are connected bytransmission paths 50 and form a network. In this example, four slavestations 30A to 30D are connected in line to the managing station 10.The managing station 10 manages the order (a logical ring) in which togive a communication right on the network and manages communication suchthat communication is performed at a predetermined communication cycle.The managing station 10 transmits, e.g., to the slave stations 30A to30D control data to drive controlled objects to be connected to theslave stations 30A to 30D at a predetermined communication cycle, andthe slave stations 30A to 30D control the controlled objects based onthe control data and transmit the status data indicating the controlstatus of the controlled objects to the managing station 10 at apredetermined communication cycle.

FIG. 2 is a diagram schematically showing an example of theconfiguration of the managing station according to the embodiment. Themanaging station 10 comprises a transmitting unit 11, a receiving unit12, a timer unit 13, a connection configuration information storing unit14, a frame processing unit 15, a delay time measuring unit 16, anaverage delay time calculating unit 17, a delay time storing unit 18, adelay detecting unit 19, an output unit 20, and a control unit 21 thatcontrols each of those units.

The transmitting unit 11 transmits frames generated by the frameprocessing unit 15 or a delay-time measurement frame (hereinafter calleda measurement frame) generated by the delay time measuring unit 16, andthe receiving unit 12 receives frames destined for its own station. Thetransmitting unit 11 and the receiving unit 12 form a communicationunit. The timer unit 13 is used when measuring a transmission delay time(hereinafter called a delay time) of each slave station 30A to 30D, isstarted when transmitting a measurement frame, and is stopped whenreceiving a delay-time measurement response frame (hereinafter called aresponse frame).

The connection configuration information storing unit 14 storesconnection configuration information (network topology information) ofthe communication apparatuses in the communication system. For example,in the communication system shown in FIG. 1, in it stored is connectionconfiguration information indicating that the slave station 30A isconnected to the managing station 10, that the slave station 30B isconnected to the slave station 30A, that the slave station 30C isconnected to the slave station 30B, and that the slave station 30D isconnected to the slave station 30C.

The frame processing unit 15 generates frames to be transmitted to theslave stations 30A to 30D and outputs them to the transmitting unit 11,and performs a reception process for making data in a frame received bythe receiving unit 12 be, e.g., usable to the other units. In normalprocessing, the frame processing unit 15 generates a synchronizationframe including control data and the like for each slave station 30A to30D at a predetermined communication cycle and obtains status data froma frame received from each slave station 30A to 30D.

The delay time measuring unit 16 measures the delay time of each slavestation 30A to 30D. Specifically, the delay time measuring unit 16generates a measurement frame and starts timing operation of the timerunit 13 when the transmitting unit 11 transmits it to one slave station30, and upon receiving a response frame that is a response to themeasurement frame from the slave station 30 by the receiving unit 12,stops timing operation of the timer unit 13 to take half of the timervalue counted by the timer unit 13 as the delay time of each slavestation 30. The delay time measuring unit 16 performs this processsequentially for all the slave stations 30A to 30D present in thenetwork based on the connection configuration information stored in theconnection configuration information storing unit 14.

The average delay time calculating unit 17 calculates an average delaytime that is a delay judgment value for each slave station 30A to 30Dusing the delay times calculated by the delay time measuring unit 16 inthe past and stores it in the delay time storing unit 18. Further, thedelay time storing unit 18 stores average delay time information inwhich the slave stations 30A to 30D are associated with their averagedelay times.

For example, as the average delay time, the average value of results ofperforming delay time measurement a predetermined number of times at thestart of the communication system may be used, after that, the averagevalue may be used fixedly until the communication system is initialized.In this case, the average delay time is not updated until thecommunication system is initialized next time.

Alternatively, as the average delay time, the average value of delaytimes measured a predetermined number of times over a period from thepresent into the past may be obtained. In this case, as to the method ofdetermining the number of times, the number of times may be variableaccording to the length of the delay time, or may be variable accordingto the amount of variation in the average value calculated. In thiscase, for example, results of measuring the delay time a predeterminednumber of times, together with the average delay time, are stored beingassociated with the slave stations 30A to 30D in the average delay timeinformation. Further, the average delay time is updated each timemeasurement is performed.

Alternatively, as the average delay time, the average value of delaytimes measured a number of times over a period from a predetermined timemay be used. Here, the predetermined time may be a time when all theslave stations 30A to 30D in the network start operating or a time whenthe occurrence of unexpected delay has been detected in any of the slavestations 30A to 30D.

The delay detecting unit 19 compares the delay time calculated by thedelay time measuring unit 16 and the average delay time stored in thedelay time storing unit 18 to determine whether a delay element hasoccurred in the network, and if detecting the occurrence of a delayelement, identifies its place. Specifically, if the delay time deviatesfrom the average delay time by a predetermined proportion, then thedelay detecting unit 19 determines that delay is occurring. Further, thedelay detecting unit 19 identifies the occurred place of the delayelement from the presence/non-presence of delay in each slave station30A to 30D and the connection configuration information indicating theconnection states of the slave stations 30A to 30D. By what degree thedelay time deviates from the average delay time when it is determinedthat delay is occurring, is decided for each network, and the referenceto determine that a delay element has occurred can be set such that ifthe delay time changes by, e.g., 10% of the average delay time or 50%thereof, the detecting unit determines so. Or, rather than detectingdelay with use of the proportion of deviation, it may be determined thatdelay is occurring if the difference between the delay time and theaverage delay time is greater than or equal to a predetermined value.

The output unit 20 outputs a warning when the delay detecting unit 19has detected the occurrence of a delay element. For example, a displayfunction (warning indication unit) such as an LED (Light-Emitting Diode)may be provided in the managing station 10 to be lit, or an LED as awarning indication unit of the slave station 30A to 30D near the placewhere a delay element has occurred or an LED as a warning indicationunit of the slave station 30A to 30D where a delay element has occurredmay be lit. Or, those LEDs may be lit at the same time. Or, where theoutput unit 20 is constituted by a display device, with the connectionrelation of each communication apparatus obtained from the connectionconfiguration information being displayed, the occurred place of a delayelement may be displayed being laid over the connection relations of thecommunication apparatuses.

The slave stations 30A to 30D used in this communication system are thesame in configuration as slave stations 30A to 30D used to realize usualsynchronous communication except that they immediately sends a responseframe destined for the managing station 10 when receiving a measurementframe, and hence description thereof is omitted.

Next, processes in this communication system will be described.Description will be made in the order of a delay time measuring process,an average delay time calculating process, and a delay detectingprocess.

<Delay Time Measuring Process>

FIG. 3 is a flow chart showing an example of the procedure of the delaytime measuring process. First, the delay time measuring unit 16 of themanaging station 10 selects one slave station 30 from the connectionconfiguration information stored in the connection configurationinformation storing unit 14 (step S11), and generates a measurementframe to be destined for that slave station 30 (step S12). Then, thedelay time measuring unit 16 has the transmitting unit 11 transmit themeasurement frame and at the same time starts timing operation of thetimer unit 13 (step S13).

The slave station 30, when having received the measurement frame (stepS14), immediately transmits a response frame to the managing station 10(step S15). At the same time that the receiving unit 12 of the managingstation 10 receives the response frame from the slave station 30 towhich it transmitted the measurement frame at step S13, the delay timemeasuring unit 16 stops timing operation of the timer unit 13 (stepS16). Then, the delay time measuring unit 16 calculates the delay timeof the slave station 30 selected at step S11 as half of the timer valueof the stopped timer unit 13 (step S17). The calculated delay time isstored being associated with the slave station 30 in the delay timestoring unit 18 (step S18). At this time, the timer value is reset.

Then, the delay time measuring unit 16 of the managing station 10determines whether the delay time is measured for all the slave stations30 in the network (step S19), and if the delay time is not measured forall the slave stations 30 (No at step S19), then the process returns tostep S11, and the above process is repeatedly performed. If the delaytime is measured for all the slave stations 30, then the process ends.

FIG. 4 is a diagram showing the outline of the delay time measuringprocess. For example, in the case of the network configuration shown inFIG. 1, the delay time measuring process is performed as shown in FIG.4. That is, at first, the managing station 10 selects the slave station30A and transmits a measurement frame 110 to the slave station 30A andat the same time starts timing operation of the timer unit 13. Whenhaving received the measurement frame 110, the slave station 30Aimmediately transmits a response frame 111 to the managing station 10.When having received the response frame 111, the managing station 10stops timing operation of the timer unit 13. Then, the managing station10 calculates a half of the timer value as the delay time of the slavestation 30A and stores the calculated delay time.

Then, the managing station 10 selects the slave station 30B, and using ameasurement frame 112 and a response frame 113 likewise between itselfand the slave station 30B, calculates the delay time of the slavestation 30B and stores the delay time. Subsequently, the managingstation 10 sequentially selects the slave stations 30C, 30D, andlikewise calculates the delay times of the slave stations 30C, 30D andstores them. After storing the delay time of the slave station 30D, themanaging station 10 finishes the delay time measuring process because noother slave station exists in the network.

<Average Delay Time Calculating Process>

Here, description will be made taking as an example the case where theaverage delay time is calculated after the delay time measuring processis performed a predetermined number of times like the case where theaverage delay time calculating process is performed after thecommunication system is initialized.

FIG. 5 is a flow chart showing an example of the procedure of theaverage delay time calculating process. First, the delay time measuringunit 16 of the managing station 10 performs the delay time measuringprocess (step S31). This delay time measuring process is the processshown in the flow chart of FIG. 3. Then, the delay time measuring unit16 of the managing station 10 determines whether the delay timemeasuring process has been performed a predetermined number of times(step S32). If the delay time measuring process has not been performed apredetermined number of times (No at step S32), then the delay timemeasuring unit 16 returns to step S31. If the delay time measuringprocess has been performed a predetermined number of times (Yes at stepS32), then the average delay time calculating unit 17 takes the averageof the delay times for the predetermined number of times stored in thedelay time storing unit 18 for each slave station 30 to obtain theaverage delay time (step S33). Then, the average delay times are storedbeing associated with the slave stations 30 in the delay time storingunit 18 (step S34), and the average delay time calculating processfinishes.

<Delay Detecting Process>

FIG. 6 is a flow chart showing an example of the procedure of the delaydetecting process. First, the delay time measuring unit 16 of themanaging station 10 performs the delay time measuring process (stepS51). This delay time measuring process is the process shown in the flowchart of FIG. 3. Then, the delay detecting unit 19 selects one slavestation 30 from the connection configuration information stored in theconnection configuration information storing unit 14 (step S52), andcompares the delay time calculated by the delay time measuring processand the average delay time in the delay time storing unit 18 todetermine whether unexpected delay is occurring (step S53).

If unexpected delay is not occurring (No at step S53), it is determinedthat that slave station 30 is in a normal state (step S54). On the otherhand, if unexpected delay is occurring (Yes at step S53), it isdetermined that unexpected delay is occurring in that slave station 30(step S55).

Thereafter or after step S54, it is determined whether the delaydetecting process has been performed for all the slave stations 30 (stepS56), and if the delay detecting process has not been performed for allthe slave stations 30 (No at step S56), then the process returns to stepS51.

If the delay detecting process has been performed for all the slavestations 30 (Yes at step S56), then it is determined whether there is atleast one slave station 30 in which unexpected delay has been detected(step S57). If there is no slave station 30 in which unexpected delayhas been detected (No at step S57), then it is determined that thecommunication system is in a normal state where an unexpected delay isnot occurring as much as to cause loss of synchronization (step S58).Then, it is determined whether a predetermined time has passed since ameasurement frame was transmitted last time (step S59), and if thepredetermined time has not passed (No at step S59), then the delaydetecting unit 19 goes into a wait state. If the predetermined time haspassed (Yes at step S59), then the process returns to step S51.

On the other hand, if there is at least one slave station in whichunexpected delay has been detected at step S57 (Yes at step S57), thenit is determined that in the communication system, so much unexpecteddelay is occurring as to cause loss of synchronization (step S60). Then,the delay detecting unit 19 identifies the position of the delay elementusing the connection configuration information stored in the connectionconfiguration information storing unit 14 (step S61). For example, itcan be thought that on the connection configuration information, thedelay element exists at the boundary between a slave station 30 in whichunexpected delay has been detected and a slave station 30 in whichunexpected delay has not been detected or that the delay element existsin the slave station 30 in which unexpected delay has been detected thatis the closest to that boundary. Then, the delay detecting unit 19outputs the position information of the slave station 30 close to thedelay element (step S62). For example, in the above example, the slavestation 30 in which unexpected delay has been detected and the slavestation 30 in which unexpected delay has not been detected on oppositesides of the above boundary are acquired as slave stations 30 close tothe delay element. Then, the output unit 20 of the managing station 10can light a warning indication light such as an LED provided in its ownstation, or light a warning indication light such as an LED provided inthe slave station 30 in which unexpected delay has been detected, ordisplay a connection state diagram based on the connection configurationinformation on a displaying unit such as a liquid crystal displayprovided in its own station and display the occurred place of the delayelement laid over the diagram. This finishes the delay detectingprocess.

Note that if unexpected delay has been detected, the delay detectingunit 19 of the managing station 10 may stop communication in thecommunication system, or the delay detecting unit 19 of the managingstation 10 may store, as a new average delay time, the delay timecalculated at step S51 for the slave station 30 where delay isdetermined to have occurred in the delay time storing unit 18 so as toperform the delay detecting process based on that value. Further, thedelay detecting unit 19 can efficiently identify the occurred place ofthe delay element by performing the delay time measuring process in theorder from a slave station 30 closest to the delay element using theconnection configuration information.

FIG. 7 is a diagram schematically showing an example of the operation ofthe communication system in the case where a delay element has occurredon the network. Here, it is assumed that in the communication system ofFIG. 1, some delay element 140 has occurred between the slave stations30B and 30C. That is, delay times calculated from measurement of thetime from when the managing station 10 transmits measurement frames 110,112 respectively to the slave stations 30A and 30B to when receivingresponse frames 111, 113 are within a predetermined range as comparedwith the average delay times of the slave stations 30A and 30B stored inthe delay time storing unit 18. In contrast, delay times calculated frommeasurement of the time from when the managing station 10 transmitsmeasurement frames 114, 116 respectively to the slave stations 30C and30D to when receiving response frames 115, 117 are detected to greatlydeviate from the predetermined range as compared with the average delaytimes of the slave stations 30C and 30D stored in the delay time storingunit 18. At this time, unexpected delay is not occurring in the slavestation 30B, and unexpected delay is occurring in the slave station 30C.Hence, it is determined that the delay element 140 is occurring on thetransmission path 50 between the slave stations 30B and 30C or in theslave station 30C. Then, a warning indicating the occurrence of thedelay element 140 is output to the output unit 20. For example, awarning indication light 150 provided in the managing station 10 may belit, or warning indication lights 151, 152 provided in the slave station30B and/or the slave station 30C close to the occurred place of thedelay element 140 may be lit.

Note that, although in the above example description has been made ofthe network configuration where the managing station 10 and the slavestations 30A to 30D are connected in line, the present invention is notlimited to this, but can be applied to star-type networks and line-typestar-type mixed networks.

FIG. 8 is a diagram schematically showing an example of the operation ofthe communication system in the case where a delay element has occurredon a line-type star-type mixed network. This example shows one where ahub 60 is provided between the slave stations 30A and 30B in the networkof FIG. 1 and where slave stations 30E to 30G are further connected inline to the hub 60. After the delay time measuring process is performedon the slave stations 30A to 30D in the same way as described withreference to FIGS. 4 and 7, the delay time measuring process isperformed sequentially on the slave stations 30E to 30G with measurementframes 120, 122, 124 and response frames 121, 123, 125 thereto beingtransmitted/received.

Here, it is assumed that some delay element 141 has occurred between theslave stations 30E and 30F. That is, a delay time calculated frommeasurement of the time from when the managing station 10 transmits ameasurement frame 120 to the slave station 30E to when receiving aresponse frame 121 is within a predetermined range as compared with theaverage delay time of the slave station 30E stored in the delay timestoring unit 18. In contrast, a delay time calculated from measurementof the time from when the managing station 10 transmits a measurementframe 122 to the slave station 30F to when receiving a response frame123 is detected to greatly deviate from the predetermined range ascompared with the average delay time of the slave station 30F stored inthe delay time storing unit 18. At this time, unexpected delay is notoccurring in the slave station 30E, and unexpected delay is occurring inthe slave station 30F. Hence, it is determined that the delay element141 is occurring on the transmission path 50 between the slave stations30E and 30F or in the slave station 30F. Then, a warning indicating theoccurrence of the delay element 141 is output to the output unit 20. Forexample, a warning indication light 150 provided in the managing station10 may be lit, or warning indication lights 153, 154 provided in theslave station 30E and/or the slave station 30F close to the occurredplace of the delay element 141 may be lit.

This embodiment has the effect that if unexpected delay has occurred onthe network because of a failure in or addition of a slave station 30,it can be immediately determined where the delay element has occurredand that the occurred place of the delay element can be shown visuallyby warning indication.

INDUSTRIAL APPLICABILITY

As described above, the communication apparatus according to thisinvention is useful for networks where data is exchanged periodically.

REFERENCE SIGNS LIST

-   -   10 Managing station    -   11 Transmitting unit    -   12 Receiving unit    -   13 Timer unit    -   14 Connection configuration information storing unit    -   15 Frame processing unit    -   16 Delay time measuring unit    -   17 Average delay time calculating unit    -   18 Delay time storing unit    -   19 Delay detecting unit    -   20 Output unit    -   21 Control unit    -   30, 30A to 30G Slave station    -   50 Transmission path    -   60 Hub

The invention claimed is:
 1. A communication apparatus connected to aplurality of slave stations via a network, comprising: a transmitter anda receiver configured to communicate with the plurality of slavestations; and a processor configured to: in response to the transmittertransmitting a delay time measurement frame to each of the plurality ofslave stations and the receiver receiving a response frame to the delaytime measurement frame from said each of the plurality of slavestations, measure, for said each of the plurality of slave stations, anelapsed time from a first point in time in which the transmittertransmitted the delay time measurement frame to a second point in timein which the receiver received the response frame, and calculate anindividual delay time for said each of the plurality of slave stationsbased on the measured elapsed time for said each of the plurality ofslave stations, compare said individual delay time for said each of theplurality of slave stations with an individual delay judgment value,wherein the individual delay judgement is an average of individual delaytimes calculated in previous communication cycles for a respective slavestation, wherein the individual delay time of a current cycle isreceived after the individual delay times of the previous communicationcycles, determine whether an abnormal delay is occurring in at least oneof the plurality of slave stations, in response to the determining thatthe abnormal delay is occurring, identifying a position of a delayelement using connection configuration information indicating connectionstates between the communication apparatus and the plurality of slavestations in the network, and in response to the determining that theabnormal delay is not occurring, updating the individual delay judgementby recalculating the average of the individual delay times using thecalculated individual delay time of the current communication cycle andthe delay times of the previous communication cycles, wherein, inresponse to the identified delay element being in a faulty slave stationfrom among the plurality of slave stations, the transmitter transmits awarning indication to the faulty slave station in which the determinedabnormal delay has been identified, wherein, in response to theidentified delay element being not in one of the plurality of slavestations and being between two of the plurality of slave stations, thetransmitter transmits the warning indication to an adjacent slavestation from among the plurality of slave stations, which is adjacent tothe identified delay element, and wherein, in response to the warningindication, one of the faulty slave station and the adjacent slavestation is configured to output an alarm showing an occurrence of thedetermined abnormal delay.
 2. The communication apparatus according toclaim 1, further comprising: a display configured to display theidentified position of the delay element on a diagram of the connectionstates between the communication apparatus and the plurality of slavestations based on the connection configuration information.
 3. Thecommunication apparatus according to claim 1, wherein: in response tothe calculated individual delay time deviating from the individual delayjudgment value by a predetermined amount or proportion, the processor isfurther configured to set the calculated delay time as a new delayjudgment value for the respective slave station.
 4. The communicationapparatus according to claim 1, wherein the network is at least one of:a line type network and a star type network.
 5. A communication methodin a communication system where a managing station and a plurality ofslave stations are connected via a network, the method comprising:transmitting, by the managing station, a delay time measurement frame toa slave station from the plurality of slave stations; starting a timingoperation in response to the transmitting of the delay time measurementframe to measure an elapsed time; receiving, by the managing station, aresponse frame responsive to the delay time measurement frame from theslave station; stopping the timing operation in response to thereceiving of the response frame to measure the elapsed time; calculatinga delay time of the slave station in a current communication cycle,based on the measured elapsed time; comparing the calculated delay timewith a delay judgment value that is an average of individual delay timescalculated in previous communication cycles using the timing operationfor the slave station, wherein the calculated delay time of the currentcycle is received after the individual delay times of the previouscommunication cycles; determining whether an abnormal delay is occurringin the slave station based on the comparing; in response to thedetermining indicating that the abnormal delay is occurring in the slavestation, identifying a position of a delay element using connectionconfiguration information indicating connection states between themanaging station and the plurality of slave stations in the network; andin response to the determining indicating that the abnormal delay is notoccurring, updating the delay judgment by recalculating the average ofthe individual delay times using the calculated delay time in thecurrent cycle and the individual delay times of the previouscommunication cycles, wherein the transmitting, the starting, thereceiving, the stopping, the calculating, the comparing, and thedetermining is performed for each of the slave stations, wherein, inresponse to the identified delay element being in a faulty slave stationfrom among the plurality of slave stations, transmitting a warningindication to the faulty slave station in which the determined abnormaldelay has been identified, wherein, in response to the identified delayelement being not in one of the plurality of slave stations and beingbetween two of the plurality of slave stations, transmitting the warningindication to an adjacent slave station from among the plurality ofslave stations, which is adjacent to the identified delay element, andwherein, in response to the warning indication, one of the faulty slavestation and the adjacent slave station is configured to output an alarmshowing an occurrence of the determined abnormal delay.
 6. Thecommunication method according to claim 5, further comprising:displaying the identified position of the delay element on a diagram ofthe connection states between the communication apparatus and theplurality of slave stations based on the connection configurationinformation.
 7. The communication method according to claim 5, whereinthe determining comprises, in response to the calculated delay timedeviating from the delay judgment value by a predetermined amount orproportion, setting the calculated delay time as a new delay judgmentvalue.
 8. The communication method according to claim 5, wherein thenetwork is at least one of a line type network and a star type network.9. The communication apparatus according to claim 1, wherein thecommunication apparatus manages the network which forms a logical ringcomprising the plurality of slave stations, communicates with theplurality of slave stations in a predetermined communication cycle, andsynchronizes the plurality of slave stations.
 10. The communicationapparatus according to claim 1, wherein a faulty slave station is aslave station that is closer to the delay element than the remainingslave stations from the plurality of slave stations.
 11. Thecommunication apparatus according to claim 1, wherein the transmittersequentially transmits the delay time measurement frame to said each ofthe plurality of slave stations and wherein the processor furthercomprises a timer which measures the elapsed time from a respectivedelay time measurement frame to a response frame for the respectiveslave station for said each of the plurality of slave stations andwherein the transmitter transmits to said each of the plurality of slavestations a synchronization frame to synchronize operations of theplurality of slave stations with each other.
 12. The communicationapparatus according to claim 1, in response to the processor determiningthat at least two of the plurality of slave stations have the determinedabnormal delay, the processor identifying the position of the delayelement as occurring in a line between a first slave station without thedetermined abnormal delay and a second slave station, which has thedetermined abnormal delay and which is closest to the communicationapparatus based on the connection configuration information.
 13. Thecommunication apparatus according to claim 1, wherein said each of theplurality of slave stations comprise a display configured to display awarning in response to the transmitter transmitting an indicator of thedetermined abnormal delay.
 14. The communication apparatus according toclaim 13, wherein the display is further configured to display a networktopology with a location identifier of the identified position of thedelay element based on receiving from the communication apparatus theidentified position of the delay element.
 15. The communication methodof claim 5, wherein the identifying is performed after the transmitting,the starting, the receiving, the stopping, the calculating, thecomparing, and the determined is performed for said each of the slavestations.
 16. The communication method of claim 5, wherein the managingstation maintains synchronization between the plurality of slavestations via transmitting a synchronization frame to said each of theplurality of slave stations, communicates with the plurality of slavestations in a predetermined communication cycle, and manages a logicalring on the network comprising at least one hub.